Magnetic resonance imaging (MRI) is the gold-standard modality for localizing myocardial scar. MRI assessment of myocardial viability prior to revascularization has been well described. The ability to distinguish endocardial, mid-myocardial, and epicardial scar using MRI could also significantly improve the targeting of ventricular arrhythmia ablation, which is challenging using currently available technology and techniques. However, many patients in need of viability assessment and ventricular arrhythmia ablation also have variations in magnetic susceptibility in the chest due to pacemakers and, in particular, implantable cardiac defibrillators (ICDs). High quality MRI images depend on baseline magnetic field (B0) uniformity. The previously mentioned objects close to the imaging field of view significantly distort B0 leading to significant image distortion and signal loss. This image artifact commonly obscures the left ventricular anterior, septal, and lateral walls, which are important targets for revascularization and ventricular tachycardia ablation, as illustrated in FIG. 1.
Shimming is a process of optimizing the homogenicity of the magnetic field and is a standard technique for reducing the distortion and improving the resolution of MRI images. Current shimming techniques, however, are targeted at minimizing small field distortions caused by lesser susceptibility variations, such as when imaging the brain region surrounding the nasal air cavities. Devices such as pacemakers and in particular ICDs introduce a larger susceptibility variation into the magnetic field and consequently a more extensive imaging artifact.
It would therefore be advantageous to provide a device and method for a shimming technique in order to cancel large susceptibility artifacts.